Method for keyless unlocking of an access door to a closed space

ABSTRACT

The invention relates to a method for keyless unlocking of an access door to a closed space, in particular a motor vehicle, which is carried out by means of an electronic system, comprising a control module for an electronic lock, associated with the said door and a portable transponder for authorised users. The method comprises sending an interrogation signal at low frequency from the control module to the transponders and also the exchange of data at high frequency. The control module has reception means for the above which are at least continuously in a listening mode. Said method is characterised in that the low frequency transmitters are inactive in a preliminary functional mode, the high frequency transmission means in the transponder periodically emits an activation signal for said transmission means in order that the above are only activated during limited periods, which ensures the reception of an interrogation signal for a transponder entering the low frequency communication region.

[0001] The present invention concerns a “keyless” method for unlockingan access door to a closed space, in particular a car. Those skilled inthe art know several implementations and variants of such methods foropening a car door, i.e. unlocking its electronic lock, or for startingthe car, wherein the conventional contact keys or mechanical keys arereplaced by transponders or electronic RFID units. Thus, activation ofthe electronic lock is controlled via wireless communication between acontrol device associated with the door and at least one transponderintended for this application and arranged for communicating, inparticular, an identification code.

[0002] There is known from U.S. Pat. No. 4,688,036, a “keyless” accesssystem for a motor vehicle, wherein the electronic lock control device,in particular the electromagnetic signal emission and receptioncircuits, is activated only after the user has activated a manualswitch. The user in possession of an authorised transponder, thusactuates a switch arranged outside the car to activate first of all thetransmitter of the control device such that the latter can send aninterrogation signal to the transponder after having woken it. Thus,activation of the system's emission and reception circuits and thecommunication protocol for determining whether the transponder isauthorised occur between actuation of the external switch and thesending of an unlocking signal to the electronic lock.

[0003] By providing an external manual switch in the method for openinga door using a transponder, the power consumption of the door lockingcontrol device is limited, this control device being activated only fora given period of time following actuation of the external switch.

[0004] It will be noted in fact, that continuous activation of thecontrol device, particularly periodically sending an interrogationsignal to detect the presence of an authorised transponder, generateshigh energy consumption, particularly because of certain materials thatform the car. Although the energy source in a car can be large,particularly taking energy from a battery of the latter, continuousactivation of the electromagnetic signal transmission means can causethe battery in question to run down when the car is not used regularly.

[0005] U.S. Pat. No. 4,688,036 provides for the use of only onecommunication frequency and for the external switch to be arranged underthe handle of the door concerned.

[0006] DE Patent No. 198 27 586 discloses a more improved access systemto a car, wherein low frequency (LF) and high frequency (HF)communication is provided, so as to increase the transmission speed ofencoded data between the electronic door unlocking device and anauthorised transponder, the validly detected presence of which causessaid door to open. The speed of such communication is particularlyimportant within the scope of the main proposed embodiment where thetransmission circuit for an interrogation signal is activated byactuating the handle used for opening the door. It is thus preferable,in such an embodiment, for the electronic lock to be opened quickly;otherwise the user will find the door locked first of all when he pullsthe handle to open the door.

[0007] It will be noted that the low frequency transmitter isessentially used for sending the interrogation signals to thetransponders in a limited area, close to the door.

[0008] As shown in FIG. 1 annexed hereto, the reception area for an LFinterrogation signal by a transponder defines approximately asemi-circle 2 with a radius of 1.5 to 2 m around antenna 6 arranged in adoor of car 8. However, the high frequency communication circle 4between transponder 10 and the HF receiver arranged in the car typicallyhas a radius of at least 30 m.

[0009] DE Patent No. 198 27 586 also provides for a remote actuationbutton for the electronic lock to be arranged in the transponder. Thus,when the user wishes to open a door or the doors of his car from adistance, he only need depress the button-switch of the transponder forthe latter to send an HF signal to the HF reception means of the lockcontrol device. This improved embodiment requires the HF reception meansof the control device to be permanently or almost permanently inlistening mode. Although this function requires a certain amount ofenergy, the energy consumption generated is however relatively low forthe conventional energy sources that can be arranged in cars.

[0010] DE Patent No. 198 27 586 also proposes a particular embodimentwherein no external switch is provided for activating the lock controldevice communication means, the low frequency transmission meanscontinuously sending, in a cyclical manner, an interrogation signal.Given that the communication radius is typically from 1.5 to 2 m for theLF transmitter, the door opening authorisation protocol can be startedas soon as a transponder enters the LF communication area. When a userprovided with a transponder actuates an external switch of the vehicle,the transponder is located between 0.5 and 1 m from the LF transmitter.In the case of this particular embodiment, starting from the hypothesisthat the user walks at a speed of 1 m per second, the door openingauthorisation protocol can start approximately one second before themoment when the user reaches the door handle. Thus, the communicationtime available is greatly increased such that it is possible toimplement a highly secure identification protocol and to unlock theelectronic lock before the user pulls the handle to open the door. Thisfeature increases the ease of use of the “keyless” opening system.However, currently, this embodiment is not used in practice since itgenerates high energy consumption, as was explained hereinbefore. Giventhis major problem, automobile manufacturers generally provide for thedoors of a car to be opened either by actuating the handle, or bypressing on a button-switch arranged on the surface of the transponder.

[0011] It is an object of the present invention to overcome theaforementioned problem while maintaining optimum use of the lowfrequency communication area of the control device.

[0012] The invention therefore concerns a method for unlocking an accessdoor to a closed space whose features are given in claim 1 annexedhereto.

[0013] Owing to the features of the method according to the invention,it is possible to activate the low frequency transmission means of anelectronic lock control device before the transponder penetrates thecommunication area of said transmission means, without having tomanually actuate a transponder switch. Indeed, the periodic sending ofan activation signal for the LF transmission means of the control deviceallows the hands to be kept free during the preliminary operating modeof the electronic system. This preliminary mode can be continuallyswitched one while the transponder is being powered.

[0014] The periodic sending of an activation signal for the LFtransmission means does not generate any extra power consumption for thevehicle when said control device can be activated remotely using a highfrequency signal sent by the transponder. Indeed, in such a currentlyconventional case, the HF reception means of the control device arecontinually activated. Moreover, the transponders are already fittedwith HF transmission means. As regards the power consumption of atransponder, mean power consumption for powering the LF receiving systemin listening mode consumes approximately 2 to 5 μA. If the activationsignal for the LF transmission means is sent with a repetition period ofapproximately 30 seconds, the mean extra power consumption for thetransponder can be estimated at approximately 3 μA. This extra powerconsumption is certainly significant, but remains sufficiently low toallow the functionality peculiar to the present invention to beintegrated in a door opening system answering the required criterion ofautonomy; even when the preliminary operating mode of the electronicsystem remains permanently activated at least outside the periods ofactivation of the electronic lock control device low frequencytransmission means.

[0015] The present invention will be described more preciselyhereinafter using the following description, made with reference to theannexed drawings, given by way of non-limiting examples, in which:

[0016]FIG. 1, already described, schematically shows a system forunlocking the door of a motor vehicle wherein the communication is madeat low frequency as well as at high frequency;

[0017]FIGS. 2 and 3 show respectively a control device for an electroniclock and a transponder associated therewith, which are used forimplementing the present invention; and

[0018]FIG. 4 is a diagram schematically representing various steps ofone implementation of the method of the invention.

[0019] Referring to FIGS. 2 and 3 an embodiment of an electronic systemfor implementing the method of the invention will be briefly described.

[0020] This electronic system comprises on the one hand a control device12 for at least one electronic lock 14 of an access door to a closedspace, in particular a motor vehicle and on the other hand at least onetransponder 16 intended to be worn by a person authorized to access saidclosed space, in particular to enter into said vehicle.

[0021] Device 12 comprises in particular a data management central unit20 associated with a high frequency (HF) reception circuit 22 connectedto an antenna 23 and to a low frequency (LF) transmission circuit 24connected to an antenna 25. Circuits 20, 22, and 24 are powered by abattery 26 via a power management circuit 28. Central unit 20 isconnected to a control circuit 30 for at least one electronic lock, saidcircuit being in turn electrically connected to the electronic lock(s)of the access door(s) to the closed space. In an alternative embodimentfor a particular implementation mode, a high frequency transmissioncircuit connected to antenna 23 or a similar antenna is provided.

[0022] Transponder 16 also comprises a data management central unit 36associated with an LF reception circuit 38 connected to an antenna 39and to an HF transmission circuit 40 connected to an antenna 41.Circuits 36, 38, and 40 are powered by a battery 44 via a powermanagement circuit 46. In a particular embodiment, transponder 16further comprises an HF reception circuit 48. The transpondertransmission and reception units are arranged so as to be able tocommunicate with the corresponding units of device 12. In a particularembodiment, a switch 50, which may be actuated by a button arranged atthe surface of the transponder, is provided. This switch enables toactuate from a distance an electronic device of a motor vehicleassociated with device 12, in particular an electronic lock.

[0023] The method of the invention, provides that at least a portion ofthe communication protocol between the transponder and the controldevice for the electronic lock uses at least a low frequency signal,i.e. requires a communication at low frequency and thus at a shortdistance between transponder 16 and device 12. In particular, it isprovided that device 12 sends an LF interrogation signal to thetransponder and receives in response an identification signal. Thisidentification signal may comprise various messages and should beunderstood in a broad sense. The protocol for identification andtriggering the unlocking of electronic lock can provide a combination ofdata transmitted at low frequency and also at high frequency. In theembodiment shown in FIGS. 2 and 3, only device 12 sends LF signals.

[0024] It will be noted in this context that HF is to be understood aselectromagnetic signals having a high frequency, i.e. a frequencycomprised in the HF band or in a higher frequency band, in particular inthe UHF band.

[0025] According to the invention, in a preliminary operating mode, LFtransmission means 24, 25 are inactive and HF transmission means 40, 41of the transponder(s) 10 of the system transmit periodically an HFsignal for activating the LF transmission means of device 12. By“inactive” or deactivated” it should be understood that the transmissionmeans are in a low consumption mode wherein no signal transmissionoccurs. With regard to the reception means, it should be understood thatthey are in a rest mode and not in a listening mode.

[0026] Starting from the assumption that the HF communication distanceof the system is approximately 30 m, in a first variant one can providea repetition period of the activation signal slightly greater than 5seconds. Thus, a person running towards the motor vehicle at the speedof approximately 5 m/s will send at least an activation signal to bereceived by device 12 before that person reaches the handle of the doorto open. In another variant, in order to save the electrical energy usedby the transponders, the repetition period is provided to be between 10seconds and one minute, in particular 30 seconds. This latter valueguarantees the activation of the LF transmission means for a personwalking towards the motor vehicle at the speed of approximately 1 m/s.

[0027] According to a preferred mode of implementation, the LFtransmission means of device 12 are deactivated after a determinedactivation period if no valid identification signal has been received bythe device. In this case said preliminary mode is then again selected.

[0028] Owing to the characteristics of the invention, it is possible toobtain a method for keyless unlocking an access door to a motor vehiclewhich is efficient without at the same time consuming too much energyand discharging battery 26. Preferably, an LF interrogation signal issent with a high repetition rate as soon as the LF transmission means ofdevice 12 have been activated. Thus, as soon as a transponder enters theLF communication region associated to transmission means 24, 25 theauthorisation and identification protocol for the actuation of theelectronic lock are activated. Typically the time available between thereception of the interrogation signal by the transponder and theactuation of the handle for opening the door in question is here of atleast one second. Consequently, the time available for the electroniclock unlocking protocol is at least three times longer in the case wherethe LF transmission means are activated by the beginning of theactuation of the door handle.

[0029] Consequently, one distinguishes, in the case of the methoddescribed herein, a preliminary operating mode and a detection mode, thedetection mode being provided as soon as the LF transmission means areactivated for sending periodically an interrogation signal until atleast the reception of an identification signal or in absence of such areception, until the end of said determined activation period.

[0030] According to a particular variant of the method of the invention,it is provided that when an interrogation signal is received by the LFtransmission means of transponder 16, this transponder stops sendingsaid activation signal as long as it receives low frequency signals fromdevice 12 at least periodically.

[0031]FIG. 4 shows a diagram of one implementation mode of the method ofthe invention. When the door(s) of a motor vehicle are locked and noauthorised transponder is communicating or in any other way interactingwith control device 12, the system and in particular device 12 is set ina low consumption operating mode. However, HF reception mode of device12 are in a listening mode. As long as no UHF message is received, thesystem remains in this operating mode. However, if an UHF message isreceived, this message is decoded and the destination of the message isdetermined. It may be, in the context of the method in question, eithera command for remotely unlocking the door by means of manual switch 50(FIG. 3) or an activation command for the LF transmitter of device 12,or a message foreign to the method in question. In the latter case, thesystem remains or returns in the low consumption mode. In the two othercases the validity of the command is tested and if the command is validthe corresponding action is effected, i.e. either the electronic lock isunlocked also simply designated “door opening”, or the LF transmitter isactivated which causes an interrogation signal to sent periodically.

[0032] Of course, the one skilled in the art can envisage here variousimplementation variants. In a first variant, the HF signals transmittedby the transponders can comprise a heading for the commands in order toindicate whether it is an identification signal or an activation signal.In this case, only the message heading must be read or decoded in afirst step and the following portion of the message will only be read ordecoded if the heading corresponds to a command known to the system. Inanother variant wherein the received UHF messages are directly decoded,in a preferred manner it is provided to firstly test whether it is avalid command for activating said LF transmitter, since an openingcommand via the actuation of a switch 50 is generally effected at acertain distance from the motor vehicle. Said activation signal maycontain an identification sequence which limits the transponder capableof activating the LF transmitter of the vehicle. Preferably, it isprovided that only the transponders which are authorized for a givenvehicle and identified as such can activate this LF transmitter.

[0033] In another variant, one can provide that when LF transmitter isactivated the system ignores other activation command signals and onlychecks if it is an authorised opening command signal.

[0034] It will be noted that it is possible to provide in the context ofthe method of the invention that the activation of the LF transmissionmeans of device 12 can also be achieved by the actuation of the doorhandle in question or another external switch provided for that purpose.This enables the robustness of the system to be increased and inparticular to remedy a situation wherein the transponder has notsupplied any valid activation command signal or this signal has not beenreceived for any reason.

[0035] According to a particular implementation mode, when activationsignal is received by device 12, the latter sends an acknowledgementsignal to the transponder via transmission circuit 32 (FIG. 2) totransponder 16 in which an HF reception circuit 48 is arranged. Thisacknowledgement signal is used to indicate to the transponder havingsupplied the activation signal that it has been detected. According topreferred variant, after reception of the acknowledgement signal, saidtransponder activates the LF reception means in a listening mode inorder to receive a interrogation signal. Conversely, LF receiver 38 isdeactivated at least most of the time when the system operates in saidpreliminary mode. This last characteristic is particularly advantageousin that it enables the power consumption of the transponders to bedecreased since the transponders only activate the LF listening meansduring limited periods.

[0036] According to another implementation mode of the method of theinvention, it is provided that said identification signal and saidactivation signal are respectively transmitted at first and seconddifferent frequencies of the UHF band. For that purpose, HF transmissionmeans 22, 23 are arranged with first and second listening channelscorresponding respectively to first and second frequencies. Likewise, HFtransmission means 40, 41 of transponder 16 are arranged to be able totransmit at one or the other of these frequencies. Owing to thischaracteristic, it is thus possible to differentiate the type of commandas a function of the frequency of the received signal by device 12. Thisallows the determination of the type of the received command to beeliminated and in particular to provide a heading determining this type.

[0037] In a preferred variant of this last embodiment, only the firstchannel is selected during the LF transmission means activation periodsof device 12. Thus, when these means are activated, device 12 no longerreceives activation signals from its LF transmission means.

1. Method for keyless unlocking an access door to a closed space, inparticular a motor vehicle, by means of an electronic system, comprisingon the one hand a control device (12) for an electronic lock (14) forsaid door fitted with a first data management electronic unit (20)associated to first low frequency signal transmission means (24, 25) andto first high frequency signal reception means (22, 23) and on the otherhand at least one portable transponder (16) comprising a second datamanagement electronic unit (36) associated to second reception means(38, 39) for said low frequency signals and to second transmission means(40, 41) for said high frequency signals, said method comprising sendingan interrogation signal to at least one transponder via said firsttransmission means and, in response, sending an identification signalvia said at least one transponder to control said electronic lock, saidfirst transmission means of said control device being activated by asignal sent by said second transmission means of said at least onetransponder, characterized in that, in a preliminary operating mode ofsaid system wherein said first transmission means are inactive, saidsecond transmission means periodically transmits a high frequency signalfor activating said first transmission means.
 2. Method according toclaim 1, characterised in that said activation signal is transmittedwith a repetition period greater than 5 seconds.
 3. Method according toclaim 2, characterised in that said repetition period rangessubstantially between 10 seconds and 1 minute.
 4. Method according toany of the preceding claims, characterised in that said firsttransmission means are deactivated after a determined activation periodif no valid identification signal is received, said preliminary modebeing then selected again by said electronic system.
 5. Method accordingto any of the preceding claims, characterised in that said transponderstops transmitting said activation signal as long as it receives lowfrequency signals from control device at least periodically, uponreception of an interrogation signal by said second reception means. 6.Method according to any of the preceding claims, characterised in thatupon reception of said activation signal by said first reception means,an acknowledgement signal is transmitted at high frequency with thirdtransmission means (32) of said control device, to indicate to saidtransponder having provided said activation signal that it was detected,said transponder comprising third reception means (48) for that purpose.7. Method according to claim 6, characterised in that after reception ofan acknowledgment signal, said transponder activates then said secondreception means into a listening mode, said second means beingdeactivated at least most of the time during said preliminary mode ofsaid electronic system.
 8. Method according to any of the precedingclaims, characterised in that said second transmission means sendcontrol signals whose heading indicates whether it is saididentification signal or said activation signal.
 9. Method according toany of claims 1 to 7, characterised in that said identification signaland said activation signal are respectively sent at first and secondhigh frequencies different from each other, said first reception meanshaving first and second listening channels corresponding respectively tothese first and second frequencies.
 10. Method according to claims 9,characterised in that only said first channel is selected during theperiods when said first transmission means are activated.